The 6.5mm Grendel represents what is, in the minds of many, the optimum caliber for a rifle cartridge. While it’s true that there is a distinct difference between the ‘laboratory’ and ‘the real world’, something that does not work in the laboratory will not work in the real world while the user is subject to life-or-death pressure. 6mm bullets such as the 6mmBR consistently win 600 meter and 1000 meter benchrest shooting matches. This is due to the flatter trajectory and lower recoil when compared to a more familiar champion, the 308 Winchester.

While there are whisperings in every war about either the effectiveness or the ineffectiveness of the issued firearms, this trend hit a crescendo around 2002 with reports from sources within the US Army of the ineffectiveness of the 5.56x45mm M855 against combatants in Afghanistan. This understandably set off alarm bells within the senior military leadership and technical solutions were sought to remedy the reported problem. One of the solutions to this problem is to increase the kinetic energy at the muzzle of the 5.56mm rifle. Unfortunately there are limits to the chamber pressure that is safely achievable so the most common method of increasing performance is to increase the volume of propellant that is available to be burnt.

A 6.5mm Grendel cartridge contains 30gr of propellant while a 223 Remington cartridge contains 25gr of propellant. This yields a kinetic energy at the muzzle of 1800 ft-lbf while the 223 Remington produces about 1200 ft-lbf at the muzzle. Quite an improvement in kinetic energy for a modest increase in propellant usage. While it is true that the 6.5mm family offers great sectional density and lower wind drift compared to the 30-caliber family, I must say that my primary interest in the 6.5mm Grendel is its ability to offer more effective terminal ballistics (compared to 5.56mm) when shot from an AR-15. A 30 round magazine will hold, 30 rounds of 5.56mm ammunition or 26 rounds of 6.5mm. If something big starts, staying alive long enough to shoot all 26 rounds is not always possible. While it is convenient and comfortable to think that we will be able to emerge victorious and unhurt (as portrayed in the movies), the reality of combat is usually differs from this notion. To quote Sun Tzu:

A criminal will not usually attack you if they think that you have a reasonable ability to hurt them. As such, they will attempt to utilize the element of surprise whenever possible. The ‘hit them hard’ principle is good even if the defender is not able to fully repel the attack. The more badly injured the attacker(S) are, the less effective they will be at hurting the people that the defender was trying to protect. Let’s take a look below at a simulated Femur bone that was embedded in ballistic gelatin and shot with a 223 Remington 55gr Barnes TSX bullet at 10 feet distance:

A subject with a femur similar to the one at left will be unable to run and will likely be unable to walk. This is an advantageous situation for the defender(s) because fighting requires moderate mobility most of the time. At the right is an example of the fallacy of believing that the 223 Remington / 5.56x45mm temporary cavity is capable of damaging the large bones like the femur. The center of the bullet was 0.9 inches away from the edge of the femur bone as it passed by. Since the bullet routinely expands to 0.4”, we can say that the edge of the petal was no more than 0.7 inches away from the bone simulant at the time of bullet passage. Regardless of the close proximity and the bullets high velocity, the bone was not damaged.

The velocity of tissue as it moves outward and away from the bullets line of travel is dependent largely on the initial kinetic energy of the bullet and how quickly that bullet slows down. It is reasonable to suspect that the 6.5mm Grendel, having a considerably higher kinetic energy, poses a greater likelihood of damaging structures like the femur bone with the mechanism of temporary cavitation.